Whats this?

[haguilar]

Hi we a very new to this. Got a 36 gal tank started cycling not quite 2 weeks ago. Got live sand and so far have around 30lbs of live rock. I spotted this little white round thing and just wondering what it is.

 

[AlSimmons]

It might be the skeletal remains of a Hidden Cup coral.

 

[mcgyvr]

^^ yep or tunicate maybe or sponge of sorts..
Picture is kind of grainy though so details are a bit tough to see..